Solid fuel burning appliances such as stoker stoves and furnaces for heating rooms require some means of control to have the heat output be responsive to the temperature in the space served by the appliance. Several methods have been used to accomplish this. One method is to run the stoker in an "on-off" mode where the stoker runs when the space thermostat calls for heat, and when the space thermostat is satisfied the stoker runs for some selected period and then is off for some selected period. This "on-off" operation does respond to the thermostat, but the "on-off" timing must be carefully selected to maintain the fire. Other problems with the "on-off" operation are that the fire is slow to come back to full fire after an off period, the "on-off" timing must be changed dependent on the weather, overheating of the space occurs in marginal weather when the "off" periods cannot be made longer without having the fire go out, and some fuel is wasted in letting the fire die down and then be brought back.
A problem with stove controllers is that there is always the possibility of a power interruption while the burn rate is reduced. In the "low fire" mode the average power to the stoker may not be high enough to restart the motors running the stoker. A further problem is that a stoker type appliance will not supply heat unless power is available to the stoker. The waveform of a voltage supplied by inverters can cause poor operation of speed controls.
It is an object of the present invention to overcome the drawbacks and disadvantages or prior art controllers for solid fuel stoves.